Settlement Invariant Tests

What settlement invariant tests are

Settlement invariant tests are deterministic checks that must always hold true for the settlement system, regardless of volume, timing, network, provider behavior, or user activity. They are defined as machine-checkable conditions over ledger entries and derived balances.

The purpose of these tests is to detect drift, silent mutation, hidden state, and arithmetic inconsistencies by validating that the settlement ledger remains internally coherent under replay.

Why invariants matter for trust

A settlement system is trustworthy when its correctness can be evaluated through structure rather than reputation. Invariant tests provide that structure by defining non-negotiable rules that separate valid settlement behavior from corrupted or inconsistent state.

When invariants are enforced, the system becomes auditable by replay: anyone with the ledger and the rules can detect violations without needing privileged access to implementation details.

Scope and boundary of invariant tests

Invariant tests apply only to the settlement layer: ledger entries, their ordering, and the arithmetic transitions between balances. They do not claim correctness of external inputs such as RNG outcomes, provider RTP design, or on-chain finality semantics beyond what is explicitly recorded as input evidence.

The tests validate that, given the recorded inputs, the settlement execution is deterministic, consistent, and replayable.

Ledger arithmetic invariants

For any balance-changing ledger entry, the following relationship must hold: balance_after = balance_before + delta_amount, where delta_amount is derived from the entry type and recorded amounts. This must be true in fixed minor units, with no floating-point arithmetic.

If the ledger records fees or splits, the invariant expands to include them explicitly: the sum of all debits and credits for the entry must equal the net balance delta.

Append-only and non-mutation invariants

Historical entries must never be overwritten or deleted. Corrections must appear only as new entries that reference prior entries, preserving a complete causal chain. The invariant is violated if any replay of the ledger produces different results for the same entry sequence.

This invariant ensures that the system cannot conceal changes by mutating history, and that audits remain stable over time.

Uniqueness and idempotency invariants

Every ledger entry must have a unique identity within its scope, and no external event may be applied more than once. For example, a funding transaction hash or provider round identifier, if used as a source reference, must not map to multiple settlement credits or debits unless the split is explicitly modeled and sums are preserved.

Idempotency means that reprocessing the same input evidence must not create additional balance effects. The ledger must represent at-most-once application of each causal event.

Conservation invariants for funding and settlement

Over any chosen window (session, day, month), the closing balance must reconcile from opening balance plus all recorded credits minus all recorded debits, including deposits, withdrawals, bets, payouts, bonuses, fees, and adjustments. The reconciliation is a strict equality in minor units.

This conservation invariant detects hidden value creation or loss, and it must hold independently for each account and for aggregated scopes where the model defines them.

Ordering and causality invariants

Entries must be replayed in a deterministic order. The invariant requires that causal predecessors exist before dependents: a bet settlement cannot exist before the corresponding bet is created, and an adjustment must reference an existing target entry.

Any entry that references a non-existent prior record or violates causal ordering is structurally invalid, even if its arithmetic appears correct in isolation.

Exception handling invariants

Exceptions must be explicit. If an input is missing, inconsistent, or unverifiable within the settlement layer, the system must record an exception state rather than silently posting balance changes. The invariant is violated if balances change without a corresponding valid ledger entry that explains the change.

When an exception is resolved, the resolution must be recorded as new entries with references that preserve the full reasoning chain from detection to correction.

Reproducibility invariants

Given the same ordered ledger entries and the same invariant ruleset version, the replay result must be identical across environments. This includes the same intermediate balances, final balances, and any derived reconciliation outputs.

To support reproducibility, the invariant suite itself must be versioned, and the ledger must record or be associated with the ruleset version used for settlement at the time of posting.

What an invariant violation means

An invariant violation is not a disagreement about outcomes; it is structural evidence that the ledger cannot be trusted as a deterministic representation of settlement. Violations indicate at least one of: arithmetic inconsistency, duplication of causal inputs, mutation of history, broken ordering, or untracked balance movement.

Because invariants are defined over the ledger itself, a violation is detectable without external narratives, and it can be surfaced as a machine-verifiable proof of inconsistency.